| Description |
Facies and stratigraphic analysis of the John Henry Member of the Upper Cretaceous Straight Cliffs Formation, exposed in the northern Kaiparowits Plateau of southern Utah, reveals deposition of four regressive-transgressive (R-T) cycles. Each of the four R-T cycles is discussed in detail, with emphasis on the transgressive phases of deposition. Fifteen lithofacies (LF) are grouped into four facies associations (FAs): FA-1: wave-dominated shorefaces; FA-2: coastal plain; FA-3: tide-influenced coastal margin; FA-4: low-energy bay/lagoon. Regressive deposits preserve FA-1 and FA-2, whereas FA-3 and FA-4 comprise transgressive intervals. Seven bounding surfaces and elements define the regressive-transgressive architecture: 1) maximum regressive surface (mRs); 2) process change from wave- to tide-dominated processes (pCt); 3) tidal ravinement surface (tRs); 4) wave ravinement surface (wRs); 5) flooding surface (FS); 6) tide- to fluvial-dominated process change (pCf); and 7) the subaerial unconformity (SU). At Main Canyon, a stepped, forced regression is associated with the development of shore oblique incised valleys. A composite stratigraphic surface (SU/mRs/tRs), referred to here as the ""lower John Henry Member sequence boundary,"" separates regressive shorefaces from overlying high-energy, transgressive estuarine and backbarrier deposits. Basinward, the correlative conformity is preserved as sharp-based wavedominated, river-influenced shorefaces. Overlying R-T cycles are not associated with valley incision, but instead preserve sand-rich back-barrier and tidal channel deposits which are overlain distributary mouth bars, fluvial channels and coastal plain fines, which record infilling of the back-barrier. The preservation of >30 m thick accumulations of back-barrier deposits indicate an accretionary shoreline trajectory with balanced rates of high sediment supply and accommodation. Regional correlation across the northern Kaiparowits Plateau indicate 47% expansion of the John Henry Member occurring over ~14 km from southwest to northeast, with a steep topographic gradient of 0.011. These results suggest structural deformation of the foredeep was occurring from Coniacian to Campanian time, controlling sediment transport, and depositional patterns across the Kaiparowits subbasin. Allogenic and autogenic processes are considered as controls on the stratigraphic architecture for successive regressive-transgressive cycles. This study adds to the growing body of literature documenting the complex nature of transgressive deposits, which will aid in the prediction and management of analogues subsurface reservoirs. |
